Biology subjects

Simpson, D. W.

Publications and source records attributed to Simpson, D. W..

3 recordsLinked to original sources

bioRxiv2018

Image-based Phenotyping and Disease Screening of Multiple Populations for resistance to Verticillium dahliae in cultivated strawberry Fragaria x ananassa

1.0Verticillium dahliae is a highly detrimental pathogen of soil cultivated strawberry (Fragaria x ananassa). Breeding of Verticillium wilt resistance into commercially viable strawberry cultivars can help mitigate the impact of the disease. In this study we describe novel sources of resistance identified in biparental strawberry populations, creating a wealth of data for breeders to exploit. Pathogen-informed experiments have allowed the differentiation of subclade-specific resistance responses, through studying V. dahliae subclade II-1 specific resistance in the cultivar Redgauntlet and subclade II-2 specific resistance in Fenella and Chandler.\n\nA large-scale low-cost phenotyping platform was developed utilising automated unmanned vehicles and near infrared imaging cameras to assess field-based disease trials. The images were used to calculate disease susceptibility for infected plants through the normalized difference vegetation index score. The automated disease scores showed a strong correlation with the manual scores.\n\nA co-dominant resistant QTL; FaRVd3D, present in both Redgauntlet and Hapil cultivars exhibited a major effect of 18.3 % when the two resistance alleles were combined. Another allele, FaRVd5D, identified in the Emily cultivar was associated with an increase in Verticillium wilt susceptibility of 17.2%, though whether this allele truly represents a susceptibility factor requires further research, due to the nature of the bi-parental cross.\n\nMarkers identified in bi-parental populations were validated across a set of 92 accessions to determine whether they remained closely linked to resistance genes in the wider germplasm. The resistant markers FaRVd2B from Redgauntlet and FaRVd6D from Chandler were associated with resistance across the wider germplasm. Furthermore, comparison of imaging versus manual phenotyping revealed the automated platform could identify three out of four disease resistance markers. As such, this automated wilt disease phenotyping platform is considered to be a good, time saving, substitute for manual assessment.

genetics↗

bioRxiv2018

Identification of powdery mildew resistance QTL in Fragaria x ananassa

The obligate biotrophic fungus Podosphaera aphanis is the causative agent of powdery mildew on cultivated strawberry (Fragaria x ananassa). Genotypes from two bi-parental mapping populations Emily x Fenella and Redgauntlet x Hapil were phenotyped for powdery mildew disease severity in a series of field trials. Here we report multiple QTL associated with resistance to powdery mildew, identified in ten phenotyping events conducted across different years and locations. Seven QTL show a level of stable resistance across multiple phenotyping events however many other QTL were represented in a single phenotyping event and therefore must be considered transient. One of the identified QTL was closely linked to an associated resistance gene across the wider germplasm. Furthermore, a preliminary association analysis identified a novel conserved locus for further investigation. Our data suggests that resistance is highly complex and that multiple additive sources of quantitative resistance to powdery mildew exist across strawberry germplasm. Implementation of the reported markers in marker-assisted breeding or genomic selection would lead to improved powdery mildew resistant strawberry cultivars, particularly where the studied parents, progeny and close pedigree material are included in breeding germplasm.\n\nKey MessagePowdery mildew resistance in two strawberry mapping populations is controlled by both stable and transient novel QTL of moderate effect. Some transferability of QTL across wider germplasm was observed.

pathology↗

bioRxiv2018

Quantitative Trait Loci Controlling Phytophthora cactorum Resistance in the Cultivated Octoploid Strawberry (Fragaria x ananassa)

The cultivated strawberry, Fragaria x ananassa (Fragaria spp.) is the most economically important global soft fruit. Phytophthora cactorum, a water-borne oomycete causes economic losses in strawberry production globally. A bi-parental cross of octoploid cultivated strawberry segregating for resistance to P. cactorum, the causative agent of crown rot disease, was screened using artificial inoculation. Multiple resistance quantitative trait loci (QTL) were identified and mapped. Three major effect QTL (FaRPc6C, FaRPc6D and FaRPc7D) explained 36% of the variation observed and in total, the detected QTL explained 86% of the variation observed. There were no epistatic interactions detected between the three major QTLs. Testing a subset of the mapping population progeny against a range of P. cactorum isolates revealed no major differences in host response, however, some lines showed higher susceptibility than predicted, indicating that additional undetected factors may affect the expression of some quantitative resistance loci. Using historic crown rot disease score data from strawberry accessions, a preliminary genome-wide association study of 114 individuals revealed additional loci associated with resistance to P. cactorum. Mining of Fragaria vesca Hawaii 4 v1.1 genome revealed candidate resistance genes in the QTL regions.

plant biology↗